1. Field of the Invention
The present invention relates to a high-power semiconductor laser array apparatus that is applicable to various fields, such as optical recording, optical communications, punching, and welding. The present invention also relates to a multi-wavelength laser emitting apparatus using a plurality of such semiconductor laser array apparatuses.
2. Description of the Related Art
In recent years, attempts have been made to apply semiconductor laser array apparatuses to various fields, such as optical recording, optical communications, punching, and welding. This creates demand for high-power semiconductor layer array apparatuses because currently available semiconductor laser array apparatuses are basically low-powered and are not applicable to these fields.
A high-power semiconductor laser array apparatus is disclosed by Japanese Laid-Open Patent Application No. H5-226765. The semiconductor laser array apparatus has an array structure where a plurality of semiconductor laser elements are formed on the same substrate. Note that in this specification, a semiconductor laser element refers to a laser oscillation unit including a current blocking layer.
In the semiconductor laser array apparatus, the semiconductor laser elements are arranged close to each other in the width direction thereof. This arrangement causes interference between laser lights emitted from the semiconductor laser elements, so that the laser lights are matched in wavelength and phase (so-called xe2x80x9cphase lockingxe2x80x9d is achieved). As a result, the laser lights emitted from the plurality of semiconductor laser elements are condensed to form a spot and the output power of the semiconductor laser array apparatus is increased.
To increase the flexibility in designing a semiconductor laser apparatus, it is required to develop a new structure where the phase locking is achieved without arranging the semiconductor laser elements close to each other in the width direction.
Gas lasers (such as CO2 lasers and excimer lasers) and solid lasers (such as YAG lasers) are mainly used for industrial laser emitting apparatuses that are applied, for instance, to welding and punching because these lasers have high output powers.
A laser emitting apparatus using a gas laser or a solid laser, however, inevitably increases in size due to its structure. In particular, a laser emitting apparatus using a gas laser needs to be equipped with a gas cylinder, so that the hardware scale of the laser emitting apparatus becomes large even if it is designed to process small materials. This increases the price of the laser emitting apparatus and creates a necessity for a large installation space. Also, the laser emitting apparatus consumes a large amount of electricity due to its low luminous efficiency. Further, because the gas cylinder of the laser emitting apparatus needs to be refilled, the maintenance cost is increased.
Also, the recent development in the material industry has realized various new types of works (materials to be processed using lasers). This causes a problem that the laser emitting apparatus using a gas laser or a solid laser cannot process a work produced by mixing two types of materials having different absorption coefficients for a laser of a wavelength.
The laser light emitted from a gas laser or a solid laser has a specific wavelength and it is difficult to change the wavelength. Suppose that a work has been produced from materials A and B, the material A has a high absorption coefficient for a laser light of a wavelength xcex1, and the material B has a low absorption coefficient for the laser light. In this case, it is necessary to increase a laser power to melt the material B as well. This excessively raises the temperature of the material A and thus melts unnecessary parts of the material A. Therefore, if a hole is formed in the work, the diameter of the hole becomes larger than an intended size. This results in a problem that the processing accuracy is significantly impaired.
To cope with this problem, it is preferred to also use a laser light of a wavelength xcex2, for which the material B has a high absorption coefficient. However, this is not a feasible solution because, as described above, it is difficult to change the wavelength of the laser light emitted from a multi-wavelength laser emitting apparatus using a gas laser or a solid laser.
Also in various other fields, there is demand for a multi-wavelength laser emitting apparatus of a reduced size but a high output power.
The first object of the present invention is therefore to provide a semiconductor laser array apparatus where laser lights emitted from a plurality of elements provided on the same substrate are matched in wavelength and phase (that is, the laser lights are phase locked).
The second object of the present invention is to provide a multi-wavelength laser emitting apparatus that realizes a small-sized but relatively high-power laser appliance which emits various laser lights having different wavelengths.
The first object is achieved by a semiconductor laser array apparatus including: a substrate; a plurality of current blocking elements that are stripe shaped and are formed on the substrate; and a plurality of light waveguides that are formed between the plurality of current blocking elements, where at least two adjacent light waveguides are optically connected by removing a part of each current blocking element therebetween.
This construction allows the semiconductor laser array apparatus to match emitted laser lights in wavelength and phase (that is, the laser lights are phase locked) without arranging semiconductor laser elements close to each other in the width direction thereof on the same substrate.
With the conventional technique described above, laser elements need to be arranged close to each other in an arrangement direction of light waveguides to cause interference between laser lights emitted from the laser elements. This limits the width of a current blocking layer and decreases design flexibility. Also, because the laser elements are arranged close to each other, heat is confined in a narrow space and the amount of generated heat is increased. Temperature is increased particularly in a center area and the reliability of an apparatus is reduced.
On the other hand, with the technique of the present invention, semiconductor laser elements are not arranged close to each other in the width direction thereof on the same substrate. This increases design flexibility and reduces the amount of heat generated at each laser element. As a result, the reliability of the apparatus is increased.
Also, because semiconductor laser elements are not arranged close to each other on the same substrate with the technique of the present invention, phase locking is achieved with reliability, in comparison with the conventional technique. That is, with the conventional technique where phase locking is achieved by arranging semiconductor laser elements close to each other, the phase locking cannot be achieved with reliability. However, with the technique of the present invention where light waveguides are optically connected to each other by discontinuous areas of the current blocking layer, light distribution areas are formed also in the discontiguous areas. These light distribution areas cause the interference between lights traveling through adjacent light waveguides, and thus amplify the lights. This makes it possible that phase locking is achieved with stability and reliability.
Here, the discontiguous areas of the current blocking layer may be long grooves and arranged close to the light waveguides. In this case, phase locking can be achieved without problems. This is because even if the discontiguous areas are not connected to the light waveguides, waveguide areas through which lights seep overlap the light distribution areas. Therefore, interference is caused between lights traveling through adjacent light waveguides (that is xe2x80x9ca light interference functionxe2x80x9d is achieved) and phase locking is provided.
Also, the discontiguous areas of the current blocking layer may be long grooves and formed as connection waveguides that connect the light waveguides. In this case, although light loss is caused due to the scattering of lights, phase locking is achieved with more reliability. With this construction where the discontiguous areas of the current blocking layer are formed as the connection waveguides, lights traveling through the light waveguides are scattered and introduced into the connection waveguides. Therefore, lights in the light waveguides travel also through the adjacent waveguides. This achieves the light interference function and a function of sharing resonators (hereinafter, the xe2x80x9cresonator sharing functionxe2x80x9d). As a result, phase locking is achieved with more reliability.
Here, each connection waveguide may be arranged so that an extension direction of the connection waveguide crosses extension directions of the at least two adjacent light waveguides.
Also, end parts of each connection waveguide may be bent so that the connection waveguide smoothly merges with the at least two adjacent light waveguides.
This construction reduces the amounts of lights that are scattered and lost at connections between the connection waveguides and the light waveguides.
The first object of the present invention is also achieved by a semiconductor laser array apparatus including: a substrate; a plurality of current blocking elements that are formed on the substrate; and a plurality of light waveguides that are formed between the plurality of current blocking elements, where at least two adjacent light waveguides are bent and connected via at least one point.
This construction allows the semiconductor laser array apparatus to match emitted laser lights in wavelength and phase (phase locking is achieved) without arranging semiconductor laser elements close to each other in the width direction thereof on the same substrate.
Also, with the technique of the present invention, semiconductor laser elements are not arranged close to each other in the width direction thereof on the same substrate. This increases design flexibility and reduces the amount of heat generated at each laser element. As a result, the reliability of the apparatus is increased.
Further, because semiconductor laser elements are not arranged close to each other on the same substrate, the technique of the present invention provides phase locking with reliability, in comparison with the conventional technique. That is, with the conventional technique where phase locking is achieved by arranging semiconductor laser elements close to each other, the phase locking cannot be achieved with reliability due to the unevenness of the distribution of each laser light in a horizontal direction. However, with the technique of the present invention where light waveguides are connected to each other and resonators are partially shared, phase locking is achieved with reliability by the light interference function and the resonator sharing function.
The first object of the present invention is further achieved by a semiconductor laser array apparatus including: a substrate that includes a first end face and a second end face opposing to each other; a current blocking element that is formed on the substrate, first grooves and second grooves being formed in the current blocking element, the first grooves extending in parallel from the first end face toward the second end face, and the second grooves extending in parallel from the second end face toward the first end face; first light waveguides that are respectively formed in the first grooves; and second light waveguides that are respectively formed in the second grooves, where the first and second light waveguides are alternatively arranged in an arrangement direction thereof.
This construction allows the semiconductor laser array apparatus to cause interference between emitted laser lights and to match the laser lights in wavelength and phase (phase locking is achieved) without arranging semiconductor laser elements close to each other in the width direction thereof on the same substrate.
Because this construction provides phase locking by causing interference between laser lights, the ends of opposing waveguides need to be arranged close to each other in the extension direction of the waveguides to obtain overlapping waveguide areas through which lights seep. However, unlike the conventional technique, the waveguides are not arranged close to each other in an arrangement direction of the waveguides. That is, the technique of the present invention provides phase locking with a construction that differs entirely from that of the conventional technique.
Here, the semiconductor laser array apparatus may further include: a p-type sheet electrode; and an n-type sheet electrode, where the plurality of current blocking elements and the light waveguides are sandwiched between the p-type sheet electrode and the n-type sheet electrode.
Also, the semiconductor laser array apparatus may further include: a window-mirror structure that is established at each end part of the apparatus that includes end parts of the light waveguides.
With this construction, the amounts of laser lights absorbed into the end parts of the waveguides are reduced and the amount of generated heat is decreased.
Here, the semiconductor laser array apparatus may further include: an insulating part that is formed at each area where an electric power is applied to a surface of the window-mirror structure.
This construction further decreases the amount of heat generated at the end parts of the waveguides.
Here, a forbidden band width of each current blocking element may be larger than a forbidden band width of an active layer of each light waveguide, and a refractive index of each current blocking element may be smaller than a refractive index of each light waveguide.
This construction improves laser characteristics and, for instance, reduces a threshold current value. Also, this construction makes it possible to extend waveguide areas by decreasing the amounts of laser lights absorbed into the current blocking layer. Therefore, laser lights are optically connected to each other merely by arranging the light waveguides so that their waveguide areas overlap each other. That is, it is not necessary to arrange the waveguides in close proximity to each other in the extension direction or the width direction.
The second object of the present invention is achieved by a multi-wavelength laser light emitting apparatus including: a plurality of semiconductor laser array apparatuses, each of which emits a laser light of a different wavelength; and an optical component that condenses each emitted laser light at a predetermined point, where at least one of the plurality of semiconductor laser array apparatuses includes a laser array structure where a plurality of light waveguides are formed between a plurality of current blocking elements, and at least two adjacent light waveguides are optically connected to each other.
Here, the multi-wavelength laser light emitting apparatus may further include: an adjusting unit for displacing the optical component to condense each emitted laser light at the predetermined point; a laser driving unit for selecting and exciting a semiconductor laser array apparatus that emits a laser light of a specified wavelength; and a control unit for controlling the adjusting unit according to the specified wavelength.
Here, each of the plurality of semiconductor laser array apparatuses may include: a substrate; a plurality of current blocking elements that are stripe shaped and are formed on the substrate; and a plurality of light waveguides that are formed between the plurality of current blocking elements, where at least two adjacent light waveguides are optically connected by removing a part of each current blocking element therebetween.
Here, each of the plurality of semiconductor laser array apparatuses may include: a substrate; a plurality of current blocking elements that are formed on the substrate; and a plurality of light waveguides that are formed between the plurality of current blocking elements, where at least two adjacent light waveguides are bent and connected via at least one point.
Here, each of the plurality of semiconductor laser array apparatuses may include: a substrate that includes a first end face and a second end face opposing to each other; a current blocking element that is formed on the substrate, first grooves and second grooves being formed in the current blocking element, the first grooves extending in parallel from the first end face toward the second end face, and the second grooves extending in parallel from the second end face toward the first end face; first light waveguides that are respectively formed in the first grooves; and second light waveguides that are respectively formed in the second grooves, where the first and second light waveguides are alternatively arranged in an arrangement direction thereof.